What did megalodon eat

(ORDO NEWS) — Bigtoothed sharks got their name from their huge teeth, each of which was the size of a human hand, or even more. This group includes the megalodon, the largest shark that has ever lived on earth, and several other related species.

In general, some types of sharks existed for over 400 million years long before the advent of dinosaurs. However, monster sharks with giant teeth appeared in the course of evolution after the dinosaurs died out, and continued to host in the ancient seas and oceans about three million years ago.

“We used to think that the largest species of animals, for example, blue whales, whale sharks, even elephants and diplodocus, are always natural filter feeders and at the same time herbivores, and there are no predators among them,” explains Emma Kast.

A 2019 Earth Science Graduate Emma is the lead author of a scientific paper published in the latest issue of Science Advances – But in reality, megalodon and other megatooth sharks were giant predators that ate other predators. million years ago.”

Emma Kast consultant Danny Sigman, a professor of geological and geophysical sciences at Princeton University, added: “If megalodon were swimming in the oceans now, then human interaction with the marine environment would change radically.”

A team of scientists from Princeton University have found compelling evidence that megalodon and some of its ancestors were at the top of the prehistoric food chain, which scientists call the highest trophic level. Indeed, their status, scientists believe, in a highly branched food chain was so high that they, apparently, ate other predators – both large and small.

“Ocean food webs tend to be longer than the traditional food chains of ‘plants-deer-wolves’ that land animals have, because they start out as very small organisms.

To reach the highest trophic level that the grebe shark occupied – and this super-predator reigned at the top of the ancient marine food chain – at the top of the modern marine food web, you would need to put several predators at once, ”explained Emma Kast from the University of Cambridge; note that the first version of the above Science Advances article was written by Emma while still at Princeton University and was one of the chapters of her dissertation.

The most conservative estimate is that the megalodon was about 15 meters (50 feet) long, while modern great white sharks usually reach about five meters (15 feet).

To analyze the marine food web that existed in prehistoric times, Emma Kast and Danny Sigman, along with their colleagues, applied a new method to measure nitrogen isotopes to analyze shark teeth.

As it is known (ecologists have long known), the more nitrogen-15 the body contains, the higher its position in the food chain, but scientists have never been able to measure the small amounts of nitrogen that are preserved in the enamel layer of the teeth of these extinct predators.

“We have a number of shark tooth samples from different eras. And we were able to trace the dependence of their trophic level on body size,” says Zixuan (Crystal) Rao, co-author of the above article in Science Advances. graduate student from Danny Sigman’s research group.

One way to remove an extra trophic level or two is through cannibalism, and according to some reports, this is exactly what happened in the case of megatooth sharks and other prehistoric marine predators.

Nitrogen time machine

In order to recreate the food webs of extinct creatures, perhaps only a time machine will help us – there are no other ways; after all, scientists have at their disposal only a very small number of bones with traces of teeth, and this is precisely what indicates that they were “chewed by a huge shark.”

Fortunately, Danny Sigman and his research team have spent several decades developing other methods that are based on the following principle: it turned out that the percentage of nitrogen isotopes in the cells of a living creature can determine the place in the food chain that this organism occupies (at the top , in the middle or at the very bottom).

“My research team is looking for chemically pure and well-preserved organic compounds, including nitrogen, in organisms from distant geological eras,” says Sigman.

The fact is that some plants, algae and other biological organisms that are on the bottom rung of the food web have learned to accumulate nitrogen absorbed from air or water in their tissues.

Then, they are eaten by other organisms, assimilating nitrogen; while, most importantly, they by and large excrete (sometimes with urine) a larger amount of the lighter isotope of nitrogen (N-14) than its heavier counterpart (N-15).

In other words, what happens is that as you move up the food chain, the N-15 isotope, unlike N-14, starts to accumulate in greater quantities.

In scientific research, this approach has already been used to study living organisms that lived relatively recently – somewhere around 10-15 thousand years ago. However, until recently, scientists were unable to detect enough nitrogen to make measurements in even more ancient animal remains.

Why did this happen? The fact is that soft tissues, such as muscles and skin, are almost never preserved. And with sharks, the situation is even more complicated – they do not have bones, because their skeletons are made of cartilage.

But it turns out that shark teeth are well preserved, turning into a fossil. Unlike bones, the preservation of teeth is explained by the fact that they are covered with enamel, i.e. hard material, practically immune to most types of putrefactive bacteria.

“Teeth are inherently resistant to chemical and physical influences. Therefore, being in a very chemically active environment of the oral cavity, they can not deteriorate and at the same time are able to grind food, which can consist of solid parts,” explains Sigman.

In addition, the shark does not have thirty dazzling white teeth, like a person, but more. The fact is that shark teeth grow constantly: instead of old, fallen teeth, new ones grow.

So, for example, the modern sand shark loses an average of one tooth every day, and it lives for several decades. This means that every shark has thousands of new teeth in its lifetime.

“Shark teeth are one of the most common types of fossil fossils found in geological layers,” says Sigman. “Inside the tooth, you can find a very small amount of organic matter from which tooth enamel was formed, you can say that this organic matter is now tightly sealed with enamel “.

Since shark teeth are found in large numbers and are well preserved, traces of nitrogen contained in tooth enamel can determine the status of a shark in the food web, regardless of whether this tooth fell out of the shark’s mouth – millions of years ago or just yesterday.

Even the largest tooth is covered with a thin enamel shell, in which the amount of nitrogen is too microscopic and negligible. However, the team of scientists led by Sigman did not stop developing more and more advanced methods for extracting and measuring nitrogen isotope ratios.

With the help of dental burs, special chemicals, and even microorganisms that can convert the nitrogen found inside enamel into nitrous oxide, scientists can now accurately measure the N15 to N14 isotope ratio in prehistoric teeth.

“It’s a bit like a brewery here,” Danny Sigman said. “We grow microbes and feed our samples to them. And they produce nitrous oxide for us, and we analyze it.”

During the analysis, a specially designed automated system for obtaining nitrous oxide is used, which extracts, purifies, concentrates and sends the extracted nitrous oxide to a specialized mass spectrometer just in order to determine the ratio of stable isotopes.

“For several decades, I have been trying to develop a method that could detect microscopic amounts of nitrogen,” explains Sigman.

Sigman’s group started with microfossils in geological sediments, then moved on to other types of fossilized organic remains, such as corals, auditory bones of fish and sharks. teeth. “After that, we and our colleagues began to run this method on the teeth of mammals and dinosaurs.”

Deep dive into literature during self-isolation

From the very beginning of the pandemic, while her friends baked homemade bread and swallowed Netflix, Emma Kast began to carefully study the literature on ecology. She tried to find a technique by which they measure the isotopes of nitrogen accumulated in the tissues of modern marine animals.

“It’s great that Emma decided to dig into the scientific literature, process all this information that has been published for several decades, and then apply it to the analysis of ancient fossils,” said co-author of the article Michael (Mick) Griffiths (Michael (Mick) Griffiths), paleoclimatologist and geochemist at William Patterson University.

While Emma Cast was quarantined at home, she went through a list of more than 20,000 marine mammals and more than 5,000 sharks. But she wanted more. “Our approach will help understand how ancient food webs work, which is why we need samples right now,” Kast said.

“And for this I would like to get a general idea of ​​\u200b\u200bthe ecosystem with the help of some museum or repository that has collections of ancient fossils.

I would like to have access to a collection of different types of fossils from the same era and found in the same area, ranging from some foraminifera that stand at the very base of the food web, up to otoliths (auditory ossicles) , different types of fish,

But scientists not only searched for scientific literature. They also have a collection of shark tooth specimens in their database.

Paper co-author Kenshu Shimada of DePaul University contacted aquariums and museums while other co-authors Martin Becker of William Patterson University and Harry Maisch of Florida Bay Coast University collected samples huge teeth at the bottom of the ocean.

“It’s really dangerous. Harry Maish is a master diver, and this requires a lot of experience,” explains Griffiths. you have to go down to the ocean floor. Martin Becker and Harry Maish managed to collect teeth from everywhere.”

Griffiths also added: “There has been a collaborative effort to get the samples and put them all together. All in all, working with Princeton and other regional universities is really exciting, because there are wonderful students everywhere. It was very pleasant with my colleagues work”.

Alliya Akhtar received her PhD from Princeton University in 2021 and is currently a PhD student at the Griffiths Lab.

“The work I did in the course of writing my dissertation (studying the isotopic composition of sea water) raised as many questions for me as it answered.

And I was incredibly grateful for the opportunity to continue working on some of the tasks with a colleague and mentor, whom I respect,” Akhtar wrote in an email, “I am very enthusiastic about the work that I have yet to do and the mysteries that have yet to be solved!”

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